DRAFT Inventory of U.S Greenhouse Gas Emissions and Sinks

1 2 Figure 3-5: 2015 CO2

1 2 Figure 3-5: 2015 CO2 Emissions from Fossil Fuel Combustion by Sector and Fuel Type (MMT CO2 Eq.) 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Fossil fuels are generally combusted for the purpose of producing energy for useful heat and work. During the combustion process, the C stored in the fuels is oxidized and emitted as CO 2 and smaller amounts of other gases, including CH 4, CO, and NMVOCs. 7 These other C containing non-CO 2 gases are emitted as a byproduct of incomplete fuel combustion, but are, for the most part, eventually oxidized to CO 2 in the atmosphere. Therefore, it is assumed all of the C in fossil fuels used to produce energy is eventually converted to atmospheric CO 2. Box 3-3: Weather and Non-Fossil Energy Effects on CO2 from Fossil Fuel Combustion Trends In 2015, weather conditions, and a warm first and fourth quarter of the year in particular, caused a significant decrease in energy demand for heating fuels and is reflected in the decreased residential emissions from 2014 to 2015. The United States in 2015 also experienced a warmer winter overall compared to 2014, as heating degree days decreased (10.2 percent). Cooling degree days increased significantly by 14.6 percent and despite this increase in cooling degree days, residential electricity demand decreased slightly. Warmer winter conditions compared to 2014 resulted in a decrease in the amount of energy required for heating, and heating degree days in the United States were 9.7 percent below normal (see Figure 3-6). Summer conditions were significantly warmer in 2015 compared to 2014, with cooling degree days 22.5 percent above normal (see Figure 3-7) (EIA 2016a). 8 7 See the sections entitled Stationary Combustion and Mobile Combustion in this chapter for information on non-CO2 gas emissions from fossil fuel combustion. 8 Degree days are relative measurements of outdoor air temperature. Heating degree days are deviations of the mean daily temperature below 65 degrees Fahrenheit, while cooling degree days are deviations of the mean daily temperature above 65 degrees Fahrenheit. Heating degree days have a considerably greater effect on energy demandand related emissions than do cooling degree days. Excludes Alaska and Hawaii. Normals are based on data from 1971 through 2000. The variation in these normals during this time period was 10 percent and 14 percent for heating and cooling degree days, respectively (99 percent confidence interval). 3-8 DRAFTInventoryof U.S. GreenhouseGasEmissionsandSinks: 1990–2015

1 2 Figure 3-6: Annual Deviations from Normal Heating Degree Days for the United States (1950–2015, Index Normal = 100) 3 4 5 Figure 3-7: Annual Deviations from Normal Cooling Degree Days for the United States (1950–2015, Index Normal = 100) 6 7 8 9 10 11 12 Although no new U.S. nuclear power plants were brought online in 2015, the utilization (i.e., capacity factors) 9 of existing plants in 2015 remained high at 92 percent. Electricity output by hydroelectric power plants decreased in 2015 by approximately 4 percent. In recent years, the wind power sector has been showing strong growth, such that, on the margin, it is becoming a relatively important electricity source. Electricity generated by nuclear plants in 2015 provided more than 3 times as much of the energy generated in the United States from hydroelectric plants (EIA 2016a). Nuclear, hydroelectric, and wind power capacity factors since 1990 are shown in Figure 3-8. 9 The capacity factor equals generation divided by net summer capacity. Summer capacity is defined as "The maximum output that generating equipment can supply to system load, as demonstrated by a multi-hour test, at the time of summer peak demand (period of June 1 through September 30)." Data for both the generation and net summer capacity are from EIA (2016a). Energy 3-9